For the economic utilization of C4 streams, as can be obtained, for example, from cracking processes or by dehydrogenating butanes, various processes are already known. These starting streams typically comprise relatively large amounts of 1,3-butadiene, 1-butene and 2-butenes. In addition, significant proportions of butanes, and also isobutene in the case of cracking processes, are often present. In order to achieve a very economically viable process, the individual components each have to be converted to salable products of maximum value, without the other components being impaired thereby. Particularly advantageous in this context is also the complete or partial conversion of one C4 component to another C4 component which is fed to an economically more attractive use. To this end, generally complex, multistage processes are required, in which the individual C4 components are processed stepwise. Such processes are described, for example, in DE-A-10118634, EP-A-742 195 and 742 234.
Pure 1,3-butadiene constitutes a sought-after monomer. Pure 1-butene is likewise a high-cost monomer, but after hydroformylation to valeraldehyde and subsequent aldol condensation and hydrogenation to propylheptanol also finds an economically significant outlet as a plasticizer component and surfactant alcohol. Isobutene serves as a starting material for fuel and lubricant additives after polymerization to polyisobutene, as a fuel additive after etherification with methanol to MTBE, and as knock-resistant gasoline alkylate after dimerization to diisobutene and subsequent hydrogenation. In contrast, the direct chemical reaction of 2-butenes is hitherto industrially insignificant. Here, an olefin metathesis with ethene, which converts 2-butenes to the valuable olefin monomer propene, is viable.